1. Field of the Invention
The present invention relates generally to a method and apparatus for froth flotation separation of the components of a slurry, and more particularly pertains to an improved method and apparatus for beneficiating coal by flotation separation of ground coal particles from impurities associated therewith such as ash and sulfur.
Coal is an extremely valuable natural resource in the United States because of its relative abundant supplies in this nation. It has been estimated that the United States has more energy available in the form of coal than in the combined natural resources of petroleum, natural gas, oil shale, and tar sands. Recent energy shortages, together with the availability of abundant coal reserves and the continuing uncertainties regarding the availability of crude oil, have made it imperative that methods for converting coal into a more useful energy source be developed.
2. Discussion of the Prior Art
Known prior art processes for froth flotation separation of a slurry of particulate matter are based on constructions wherein air is introduced into the liquid slurry of the particulate matter as, e.g. through a porous cell bottom or a hollow impeller shaft, thereby producing a surface froth. These prior art methods are relatively inefficient approaches especially when large concentrations of particulate matter are being processed. Generally, these techniques are inefficient in providing sufficient contact area between the particulate matter and frothing air. As a result large amounts of energy can be expended in frothing. In addition, froth flotation techniques which permit bubbles to rise in the slurry can tend to trap and carry impurities, such as ash in the froth slurry, and accordingly the such as ash in the froth slurry, and accordingly the resultant beneficiated particulate product can have more impurities therein than necessary.
Methods have been suggested and are being explored in the beneficiation of coal, i.e., the cleaning of coal of impurities such as ash and sulfur, either prior to burning the coal or after its combustion. In one recently developed technique for beneficiation, termed herein chemical surface treating, raw coal is pulverized to a fine mesh size and is then chemically treated. According to this technique the treated coal is then separated from ash and sulfur, and a beneficiated or cleaned coal product is recovered therefrom.
In further detail, in the heretofore mentioned chemical surface treating process coal is first cleaned of rock and the like, and is then pulverized to a fine size of about 48 to 300 mesh. The extended surfaces of the ground coal particles are then rendered hydrophobic and oleophilic by a polymerization reaction. The sulfur and mineral ash impurities present in the coal remain hydrophilic and are separated from the treated coal product in a water washing step. This step utilizes oil and water separation techniques, and the coal particles made hydrophobic can float in recovery on a water phase which contains hydrophilic impurities.